An apparatus for processing data and a method of data processing are provided. A processor core in the apparatus performs data processing operations in response to a sequence of instructions, including write operations which write data items to a non-volatile memory. A write-back cache stores local copies of the data items retrieved from the memory and written to the memory by the processor core. A storage unit is provided which stores indications of the write operations initiated by the processor core and the processor core is configured to respond to an end instruction by causing the local copies of data items which are the subject of the write operations by the processor core, and for which an indication is stored in the storage unit, to be cleaned from the write-back cache to the memory. The indications of the write operations stored in the storage unit are then cleared.