Described is an interlocking scheme which permits multiprocessing in a shared storage configuration with each central processing unit (CPU) having a private high-speed buffer storage utilizing the store-in-buffer concept. The basic problem solved is insuring that all processors access the latest copy of common data with minimum performance impact. The system allows fetch-only copies of the same shared storage block to exist simultaneously in all private storages, but only one private store is allowed to contain a block of data currently being stored into. Disclosed, in addition to the normal controls necessary to search a high speed buffer to determine whether or not the data required by the processor is in the buffer, is means for interconnecting the processors sharing a main storage. The interconnection is for broadcasting address information from one processor to the storage control mechanism of other processors for the purpose of invalidating data in other private storages or insuring that data obtained by one processor from the shared storage is the most current value. That is, if data has been modified in the buffer of another processor, that data must be returned to the shared storage in its modified form to insure that the one processor receives the most current data.