1. A method of processing data in a tile-based graphics system having a rendering space sub-divided into a plurality of tiles with which graphics data items are associated, the method comprising: fetching, from a graphics data memory into a cache, graphics data items which are to be used in processing one of the tiles; and reading the graphics data items from the cache for use in processing said one of the tiles, wherein the method further comprises: determining indicators for the graphics data items, wherein, for each of the graphics data items, the indicator for that graphics data item is indicative of a number of tiles with which that graphics data item is associated; determining which of the graphics data items in the cache to evict based on the determined indicators; and evicting the determined graphics data items from the cache.