1. A cache memory, comprising: a cache array including storage for copies of memory blocks; a directory of contents of the cache array; a read-claim machine that performs requested accesses to the cache array; and a store queue including a plurality of entries and a store queue controller; wherein while a store request and a barrier request older than the store request are enqueued in the store queue, the store request identifying a target memory block by a target address and specifying store data, the read-claim machine acquires coherence ownership of the target memory block of the store request; and the cache memory, after coherence ownership of the target memory block is acquired and the barrier request has been retired from the store queue, updates the cache array with the store data.