Use visibility from one camera relative to another

I want to overlay the visibility from one camera onto another. For example, given the blue camera, write to a texture a value of 0 or 1 whether a pixel on a polygon can be seen by that camera. Then sample that value in a shader relative to the main camera’s perspective and color it in black or white. How would I go about doing this?

My guess is to render depth from camera A to a render texture, then convert that to Camera B space using a projection matrix