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 the number of tiles with which that graphics data item is associated; decrementing the count of the number of tiles with which a particular graphics data item is associated, when a tile with which that particular graphics data item is associated has been processed; determining which of the graphics data items in the cache to evict based on the determined indicators, such that the graphics data items to evict from the cache are determined in dependence on the numbers of tiles with which the graphics data items are associated as indicated by the determined indicators; and evicting the determined graphics data items from the cache.