1. A processing unit coupled to a memory unit, the processing unit comprising: a processing pipeline having an optimized processing mode and configured to perform blend operations on graphics data and to read data from and write data to the memory unit; a detector configured to detect the presence of a special value in the graphics data that indicates that the graphics data is dirty, wherein the optimized processing mode is disabled if the special value is detected; and another detector configured to detect the presence of the special value in the graphics data, wherein the detector monitors for the presence of the special value in an input data stream to the processing pipeline and the another detector monitors for the presence of the special value in an output data stream from the processing pipeline.