In a multiprocessing computer where a plurality of processors, each with its own buffer memory, share a main memory, a broadcast system provides each processor the capability to query each other processor to determine whether a modified (e.g. updated) version of the desired data is located in another processor's buffer memory. The memory control unit simultaneously initiates a main memory read cycle and a broadcast signal in response to a request for data. If a modified version of the data is found to be in a buffer memory, it is transferred to the main memory by the control unit. The main memory read cycle is then changed to a write cycle so that the modified version replaces the original data. The modified data is then switched onto the memory data bus and transmitted to the requesting processor. Using this system, which only allows one buffer to contain a modified version of any data item, the requesting processor obtains the most current data in one main memory cycle in such a manner that it appears that the data is originating from main memory.