A data processing system composites graphics content, generated by an application program running on the data processing system, to generate image data. The data processing system stores the image data in a first framebuffer and displays an image generated from the image data in the first framebuffer on an internal display device of the data processing system. A scaler in the data processing system performs scaling operations on the image data in the first framebuffer, stores the scaled image data in a second framebuffer and displays an image generated from the scaled image data in the second framebuffer on an external display device coupled to the data processing system. The scaler performs the scaling operations asynchronously with respect to the compositing of the graphics content. The data processing system automatically mirrors the image on the external display device unless the application program is publishing additional graphics content for display on the external display device.