1. A method of performing a block invalidate operation comprising the steps of: determining whether a CPU memory access maps to be within the address range of a block invalidate operation; forcing a cache miss for memory accesses within said range; marking the cache line being accessed as invalid; issuing a read miss request for the access; setting a valid/invalid bit to invalid in the LRU; using said valid/invalid bit to determine whether the line so marked needs invalidated by the block invalidate operation in progress.