In a multiprocessor system, a conflict checking mechanism is implemented in the L2 cache memory. Different versions of speculative writes are maintained in different ways of the cache. A record of speculative writes is maintained in the cache directory. Conflict checking occurs as part of directory lookup. Speculative versions that do not conflict are aggregated into an aggregated version in a different way of the cache. Speculative memory access requests do not go to main memory.
 This invention was made with Government support under Contract No.: B554331 awarded by Department of Energy. The Government has certain rights in this invention 21--Speculation and transaction in a system.