Method and apparatus for filtering snoop requests using a scoreboard

A snoop filter apparatus associated with a single processing unit of a computing environment having multiple processing units, each processing unit having one or more cache memories associated therewith, said snoop filter apparatus comprising:

• a first scoreboard data structure having bit locations for tracking data that have been loaded into a cache memory of its associated processing unit in response to a cache miss;
• means for setting said bit locations in said first scoreboard data structure to indicate possibility of data located in said cache memory at a particular address;
• means for receiving snoop requests from one or more memory writing sources and decoding an address of the received snoop request;
• means for comparing said decoded address against corresponding bits set in said first scoreboard data structure;
• means for forwarding said received snoop request to said processor in response to matching of a bit set in said first scoreboard data structure, or otherwise discarding said snoop request;
• a cache wrap detection means for tracking whether every cache line has been overwritten with new cache line content in said cache memory since a prior detected cache wrap condition;
• and,
• a second scoreboard data structure having corresponding bit locations as said first scoreboard data structure, said second scoreboard data structure receiving a copy of content from said first scoreboard data structure upon detection of a cache wrap condition indicating all cache lines have been overwritten with new cache line content.