1. A computer system comprising: a plurality of processors; and a main memory coupled to the plurality of processors by an interconnect fabric, the main memory organized to store data in terms of memory blocks at least one or more of which are shared by the plurality of processors, wherein, the processors store memory blocks to which they have write access in a dirty state, at least one processor operates in a dirty-shared mode such that the at least one dirty-shared processor is configured to share memory blocks that the dirty-shared processor holds in the dirty state with one or more other processors, and at least one processor operates in a non dirty-shared mode such that the at least one non dirty-shared processor is precluded from sharing memory blocks that the non dirty-shared processor holds in the dirty state with one or more other processors.