Data processing system, cache system and method for precisely forming an invalid coherency state indicating a broadcast scope

A cache memory for a cache coherent data processing system including at least first and second coherency domains each including at least one processing unit, wherein said first coherency domain includes the cache memory and said second coherency domain includes another coherent cache memory, said cache memory comprising:

• a cache controller;
• a data array including a data storage location for caching a memory block;
• a cache directory including:
• a tag field for storing an address tag in association with said memory block;
• a coherency state field associated with said tag field and said data storage location, wherein said coherency state field has a plurality of possible coherency states including a coherency state that indicates that said address tag is valid, that said data storage location does not contain valid data, said first coherency domain does not contain said home system memory, and that, following formation of said coherency state, said memory block is cached outside of said first coherency domain.

A cache coherent data processing system, comprising:

• said first and second coherency domains each including at least one processing unit, wherein said first coherency domain includes a first cache memory and said second coherency domain includes a coherent second cache memory;
• wherein said first cache memory within said first coherency domain of said data processing system holds a memory block in a storage location associated with an address tag and a coherency state field;
• and
• wherein said coherency state field has a plurality of possible coherency states including a coherency state that indicates that said address tag is valid, that said data storage location does not contain valid data, said first coherency domain does not contain said home system memory, and that, following formation of said coherency state, said memory block is cached outside of said first coherency domain.