An apparatus and method are described for a sharing aware snoop filter. For example, one embodiment of a processor comprises: a plurality of caches, each of the caches comprising a plurality of cache lines, at least some of which are to be shared by two or more of the caches; a snoop filter to monitor accesses to the plurality of cache lines shared by the two or more caches, the snoop filter comprising: a primary snoop filter comprising a first plurality of entries, each entry associated with one of the plurality of cache lines and comprising a N unique identifiers to uniquely identify up to N of the plurality of caches currently storing the cache line; an auxiliary snoop filter comprising a second plurality of entries, each entry associated with one of the plurality of cache lines, wherein once a particular cache line has been shared by more than N caches, an entry for that cache line is allocated in the auxiliary snoop filter to uniquely identify one or more additional caches storing the cache line.