each processor in a distributed shared memory system has an associated memory and a coherence directory . the processor that controls a memory is the home processor . under certain conditions , another processor may obtain exclusive control of a data block by issuing a load lock instruction , and obtaining a writeable copy of the data block that is stored in the cache of the owner processor . if the owner processor does not complete operations on the writeable copy of the data prior to the time that the data block is displaced from the cache , it issues a victim to shared message , thereby indicating to the home processor that it should remain a sharer of the data block . in the event that another processor seeks exclusive rights to the same data block , the home processor issues an invalidate message to the owner processor . when the owner processor is ready to resume operation on the data block , the owner processor again obtains exclusive control of the data block by issuing a read - with modify intent store conditional instruction to the home processor . if the owner processor is still a sharer , a writeable copy of the data block is sent to the owner processor , who completes modification of the data block and returns it to the home processor with a store conditional instruction .