Well, in many cases it has no chance of looking the same. So I recently changed it to simply ignore all rendering to framebuffers that have not been displayed. This solved many cases of various garbage appearing on the screen where the game thought it was rendering to a location in ram that it would later use as a texture (like dynamic shadows) but really was rendering to the screen.

In most games, the result is simply that things like shadows and glow effects disappear, and it goes faster since switching render target can be expensive.