Are you stating that the mouse goes into the black bars on the sides? What games are doing this to you? All the games I have in scummvm are set to 4:3 aspect and they don't go outside the viewable screen
The only thing I could suggest is to open the NVidia control panel, go to "Adjust desktop size & position". Under the scaling tab, make sure the aspect ratio radial button is selected. Under "Perform scaling on:", choose GPU. Then check "Override the scaling mode set by games and programs"
If all that fails to fix the problem, I dunno what else to suggest since I've never run across this problem