Snoop filter for large cache using hash technique with optimal refresh algorithm

An apparatus comprising:

• a snoop filter to maintain coherency of a cache, the snoop filter comprising:
• an encoded value generator to create an encoded value from a subset of a physical address of data stored in the cache, the encoded value generator to create another encoded value from another subset of another physical address of a memory transaction;
• a snoop filter cache tag array to store the encoded value and set a corresponding state bit;
• the snoop filter to identify the another encoded value in the snoop filter cache tag array and another corresponding state bit;
• the snoop filter to initiate a snoop of the cache if the another corresponding state bit is set.

A system apparatus comprising:

• a cache and a cache tag array;
• and
• a snoop filter to maintain coherency of the cache, the snoop filter comprising:
• an encoded value generator to create an encoded value from a subset of a physical address of data stored in the cache, the encoded value generator to create another encoded value from another subset of another physical address of a memory transaction;
• a snoop filter tag array to store the encoded value and set a corresponding state bit;
• the snoop filter to identify the another encoded value in the snoop filter tag array and another corresponding state bit;
• the snoop filter to initiate a snoop of the cache if the another corresponding state bit is set;
• wherein the snoop tag array is 1/Nth a size of the cache tag array, and N is at least 2.