An apparatus comprising: data access routing circuitry responsive to a data access request received from a requesting node specifying a target address, to issue signals for triggering a selected destination node selected from among a plurality of destination nodes to service the data access request; wherein when the data access request is a read request received from the requesting node over a read request channel, the data access routing circuitry is configured to issue signals for triggering the selected destination node to provide a read response dependent on data read from a target storage location identified by the target address; when the data access request is a write request received from the requesting node over a write request channel, the data access routing circuitry is configured to issue signals for triggering the selected destination node to provide a write response confirming servicing of a write operation for writing data to the target storage location; when the data access request is at least one type of atomic data access request received from the requesting node over the write request channel, the data access routing circuitry is configured to issue signals for triggering the selected destination node to provide both the read response and the write response; the data access routing circuitry comprises resource allocation circuitry to control allocation of resource for handling data access requests which require a read response; and the resource allocation circuitry is configured to reserve a portion of the resource for handling the at least one type of atomic data access request and prevent usage of the reserved resource for handling read requests, wherein when an in-use resource level exceeds a threshold, the resource allocation circuitry is configured to reserve the remaining resource for handling the at least one type of atomic data access request. data access routing circuitry responsive to a data access request received from a requesting node specifying a target address, to issue signals for triggering a selected destination node selected from among a plurality of destination nodes to service the data access request; wherein when the data access request is a read request received from the requesting node over a read request channel, the data access routing circuitry is configured to issue signals for triggering the selected destination node to provide a read response dependent on data read from a target storage location identified by the target address; when the data access request is a write request received from the requesting node over a write request channel, the data access routing circuitry is configured to issue signals for triggering the selected destination node to provide a write response confirming servicing of a write operation for writing data to the target storage location; when the data access request is at least one type of atomic data access request received from the requesting node over the write request channel, the data access routing circuitry is configured to issue signals for triggering the selected destination node to provide both the read response and the write response; the data access routing circuitry comprises resource allocation circuitry to control allocation of resource for handling data access requests which require a read response; and the resource allocation circuitry is configured to reserve a portion of the resource for handling the at least one type of atomic data access request and prevent usage of the reserved resource for handling read requests, wherein when an in-use resource level exceeds a threshold, the resource allocation circuitry is configured to reserve the remaining resource for handling the at least one type of atomic data access request. <EOS>