1. A computer-implemented method for performing a z-culling operation within a graphics processing pipeline, the method comprising: determining a first z-range for a first portion of a coarse raster tile, wherein the first portion includes a plurality of pixels having a first set of pixel locations; retrieving from a memory a corresponding z-range related to a second set of pixel locations associated with the coarse raster tile, wherein the first set of pixel locations comprises a subset of the second set of pixel locations; comparing the first z-range to the corresponding z-range to determine whether the plurality of pixels is occluded; and if the plurality of pixels determined to be occluded, then causing the plurality of pixels to be culled, or if the plurality of pixels is determined to not be occluded, then causing the plurality of pixels to be transmitted to a fine raster unit for further processing, wherein the coarse raster tile comprises a plurality of portions, including the first portion, and the portions included in the plurality of portions are processed serially.