1. A method of data processing in a cache coherent data processing system including at least a first cache memory supporting a first processing unit and a second cache memory supporting a second processing unit, wherein said first cache memory includes a cache array and a cache directory of contents of said cache array, said method comprising: in response to said first cache memory detecting on an interconnect a broadcast operation that specifies a request address, said first cache memory determining from said operation a type of said operation and a coherency state associated with said request address; and in response to determining said type and said coherency state, said first cache memory filtering out said broadcast operation without accessing said cache directory.