Writing beyond a pointer

Data processing apparatuses and methods of data processing are disclosed wherein a processing element maintains a buffer in the memory in support of the data processing it performs. A write pointer indicates a current write location in the buffer. A cache holds copies of the data which are subject to the data processing operations and allocations into the cache from the memory and write-backs from the cache to the memory are performed in cache line units of data. When the processing element performs a data write to the buffer at a location determined by the write pointer, the processor updates the write pointer in an update direction corresponding to a progression direction of data writes in the buffer, and further locations in the progression direction in the buffer between the location indicated by the write pointer and a boundary location are signalled to be written with a predetermined value.