A data processing apparatus and method of processing data are disclosed according to which a processor unit is configured to issue write access requests for memory which are buffered and handled by a memory access buffer. A cache unit is configured, in dependence on an allocation policy defined for the cache unit, to cache accessed data items. Memory transactions are constrained to be carried out so that all of a predetermined range of memory addresses within which one or more memory addresses specified by the buffered write access requests lie must be written by the corresponding write operation. If the buffered write access requests do not comprise all memory addresses within at least two predetermined ranges of memory addresses, and the cache unit is configured to operate with a no-write allocate policy, the data processing apparatus is configured to cause the cache unit to subsequently operate with a write allocate policy.