AE Adjustment Layer Separate Effects on It & Its inverse
The easiest way is to use Track Mattes. This will let you use one layer to automatically 'mask' another layer without the need for manual masking. 

Take your square adjustment layer and make any effect changes you want, then create a new adjustment layer (make sure its comp size to fit fully over the video). Place this new layer (background adjustment layer) below your screen adjustment layer. 

Select the background adjustment layer and set the Track Matte to Alpha Inverted. This action will turn automatically turn off the visibility of the top layer which is normally the desired effect, but in this case we want to turn it back on. You should end up with a layer panel looking something like this:



What this has done is the background adjustment layer is using the screen adjustment layer as a window. So wherever the screen layer is, the background layer wont be visible.