Modelling Mode CubeGrid - removing materials

Hi

I’ve recently started playing around with the Modelling Mode, specifically the CubeGrid tool. I’ve just been getting familiarised with the controls. However, I can’t seem to figure out how to remove a material assigned to an area deleted. I’ve assigned a basic material whilst blocking out an environment, but when I remove geo, the material is left behind, like in this example:

How can I remove that material from that area on the ground so it’s the checkered floor again?

Thanks