1. Command/control click the first mask in the Layers panel to load it as a selection (Cmd click on a Mac)
2. Command/Control Shift click the second mask in the Layers panel to add to the existing selection (Cmd Sh click on a Mac)
   (At this point you will see marching ants around both selections. Don’t deselect.)
3. Layer > Layer Mask > Delete
4. Layer > Layer Mask > Reveal Selection