A cache coherent data processing system includes at least first and second coherency domains each including at least one processing unit. The first coherency domain includes a first cache memory and a second cache memory, and the second coherency domain includes a remote coherent cache memory. The first cache memory includes a cache controller, a data array including a data storage location for caching a memory block, and a cache directory. The cache directory includes a tag field for storing an address tag in association with the memory block and a coherency state field associated with the tag field and the data storage location. The coherency state field has a plurality of possible states including a state that indicates that the memory block is possibly shared with the second cache memory in the first coherency domain and cached only within the first coherency domain.