Material that punches transparent hole in camera's view?

Forgive me if the answers are out there already, but I've looked and can't find an answer that I'm able to understand for exactly this purpose. I'm not familiar with shaders, stencils, culling, or anything.

What I have right now is a scene with two cameras, and using camera depths, one view is on top of the other. I want to make a material that will punch a transparent hole in the highest depth camera view so that the other camera view shows behind it. I haven't found any default shaders that can do this, so I might have to mess with the shader language some. I've looked at tutorials for stencil buffers which seem to do a similar thing, but I haven't really been able to follow any of them, and even those don't seem to have this exact purpose in mind.

I'm not sure which of these words is most appropriate to describe what I'm trying to do, but I've tried searching for answers related to "culling," "alpha over," "stencil," "mask," etc.