Patent ID: 7418558

Claim:
An information processing system that snoops memory, said information processing system having a plurality of system control apparatuses, each of said system control apparatuses comprising: a local port that holds a memory access request received from outside the system control apparatus but not from another system control apparatus, outputs the memory access request, and reoutputs the memory access request that it holds upon receiving an error retry instruction; a broadcast output section that broadcasts the memory access request output by said local port to other system control apparatuses; a broadcast input section that receives the memory access request that has been broadcast; a global port that holds the memory access request received by said broadcast input section, and outputs the memory access request; and a snoop control section that receives the memory access request from the global port, performs snooping with respect to the received memory access request and transmits cache status information containing a check result of said snooping to the other system control apparatus, wherein said snoop control section detects a synchronization error between the system control apparatus and the other system control apparatuses based on cache status information received from the other system control apparatuses, and if a synchronization error occurs, said snoop control section outputs said error retry instruction to said local port holding the memory access request whose broadcast resulted in detecting the synchronization error.