An apparatus comprising: a first bus; a first plurality of requestors (405a...405n) coupled to the first bus; a first arbitrator coupled to the first plurality of requestors to receive from the first plurality of requestors access requests which each request a respective access to the first bus, the first arbitrator further to perform a first arbitration based on the access requests, the first arbitration to select a first requestor of the first plurality of requestors, the first arbitrator further to send, based on the first arbitration, a first grant message to trigger a carrying of a first message on the first bus, the first message exchanged by the first requestor; a second bus coupled to the first arbitrator, wherein the first grant message further to trigger a carrying of the first message on the second bus; a grant order queue to receive the first grant message from the first arbitrator and to store the first grant message, the grant order queue further to provide the first grant message to trigger the carrying of the first message on the second bus; a second plurality of requestors (445a...445m); a second arbitrator to receive from the second plurality of requestors access requests which each request a respective access to the second bus, the second arbitrator to provide to the grant order queue a second grant message based on an arbitrating of the access requests received from the second plurality of requestors; and grant order logic to place grant messages in the grant order queue according to an order in which they were received at the grant order logic; wherein: the first requestor is coupled directly to the first bus, and wherein the first arbitrator to send the first grant message to the first requestor to trigger the carrying of the first message on the first bus, or the first arbitrator to send the first grant message to a common interface to trigger the carrying of the first message on the first bus, the common interface coupling the first plurality of requestors each to the first bus. a first bus; a first plurality of requestors (405a...405n) coupled to the first bus; a first arbitrator coupled to the first plurality of requestors to receive from the first plurality of requestors access requests which each request a respective access to the first bus, the first arbitrator further to perform a first arbitration based on the access requests, the first arbitration to select a first requestor of the first plurality of requestors, the first arbitrator further to send, based on the first arbitration, a first grant message to trigger a carrying of a first message on the first bus, the first message exchanged by the first requestor; a second bus coupled to the first arbitrator, wherein the first grant message further to trigger a carrying of the first message on the second bus; a grant order queue to receive the first grant message from the first arbitrator and to store the first grant message, the grant order queue further to provide the first grant message to trigger the carrying of the first message on the second bus; a second plurality of requestors (445a...445m); a second arbitrator to receive from the second plurality of requestors access requests which each request a respective access to the second bus, the second arbitrator to provide to the grant order queue a second grant message based on an arbitrating of the access requests received from the second plurality of requestors; and grant order logic to place grant messages in the grant order queue according to an order in which they were received at the grant order logic; wherein: the first requestor is coupled directly to the first bus, and wherein the first arbitrator to send the first grant message to the first requestor to trigger the carrying of the first message on the first bus, or the first arbitrator to send the first grant message to a common interface to trigger the carrying of the first message on the first bus, the common interface coupling the first plurality of requestors each to the first bus. the first requestor is coupled directly to the first bus, and wherein the first arbitrator to send the first grant message to the first requestor to trigger the carrying of the first message on the first bus, or the first arbitrator to send the first grant message to a common interface to trigger the carrying of the first message on the first bus, the common interface coupling the first plurality of requestors each to the first bus.