Cache control system

Cache control system for a private cache in a multiprocessor data processing system comprising a plurality of processors each connected to a shared bus via similar private caches, the cache control system co-operating with similar cache control systems provided for other private caches in the data processing system, the cache control system comprising: a controller for monitoring signals on the shared bus and, when data shared between ones of the processors is modified in the cache, for performing one of two or more types of data consistency procedures for the shared data; and means for determining the relative likelihood of access to the shared data by the processor corresponding to the private cache and other processors in the system, the type of data consistency procedure performed by the controller being dependent on the results of the determination.