A probe filter determines whether to issue a probe to at least one other processing node in response to a memory access request, and includes a region probe filter directory, a line probe filter directory, and a controller. The region probe filter directory identifies regions of memory for which at least one cache line may be cached in a data processing system and a state of each region, wherein a size of each region corresponds to a plurality of cache lines. The line probe filter directory identifies cache lines cached in the data processing system and a state of each cache line. The controller accesses at least one of the region probe filter directory and the line probe filter directory in response to a memory access request to determine whether to issue the probe, and does not issue any probe in response to a read-only request.