1. A method of filtering snoop traffic in a multiprocessor computing system, each processor in the multiprocessor computing system coupled to a shared main memory, the method comprising: receiving, by a cache controller, a snoop message that identifies an address in the shared memory; determining, by the cache controller, whether a set in a high level cache that maps to the address in shared memory has been bypassed by an entry in a low level cache; and responsive to determining that the set in the high level cache has not been bypassed by an entry in the low level cache, discarding, by the cache controller, the snoop message.