1. A method of data processing in a data processing system including a memory hierarchy, said method comprising: a processor core executing a storage-modifying memory access instruction to determine a memory address; and the processor core transmitting to a cache memory within the memory hierarchy a storage-modifying memory access request including the memory address, an indication of an memory access type, and, if present, a partial cache line hint signaling access to less than all granules of a target cache line of data associated with the memory address; in response to the storage-modifying memory access request: the cache memory performing a storage-modifying access to all granules of the target cache line of data if the partial cache line hint is not present; and the cache memory performing a storage-modifying access to less than all granules of the target cache line of data if the partial cache line hint is present.