1. A graphics processing system comprising: a processing module configured to receive primitives to be processed for a tile of a rendering space having one or more tiles, wherein the processing module is configured to perform hidden surface removal for primitives of the tile to determine primitive identifiers identifying the primitives which are visible at each of a plurality of sample positions in the tile; a set of two or more tag buffers configured to store the primitive identifiers determined for each of the sample positions in the tile, wherein primitive identifiers stored at corresponding sample positions in the tag buffers of the set represent overlapping layers of primitives; a tag control module configured to control: (i) selection of a tag buffer for the storage of each of the primitive identifiers identifying primitives which are determined to be visible by the hidden surface removal, wherein the selection of a tag buffer is made for a block of one or more sample positions according to the layering of the primitives identified by the primitive identifiers stored in the tag buffers at the one or more sample positions in the block, and (ii) flushing of primitive identifiers from one or more of the set of tag buffers; and a texturing engine configured to receive flushed primitive identifiers and to apply texturing to the primitives identified by the flushed primitive identifiers.