You can use layers to control what content is lit by which lights.
Here I've built a room with two shells of geometry cladding: the exterior shell is in the Default layer, and the interior shell is in a new layer I called Interior.
My red point light's culling mask is set to light only the Interior layer.
My directional sunlight's culling mask is set to light every layer except the Interior.
I also edited my scene settings to drop the "Environment Lighting" ambient multiplier to zero, and added a couple of extra directional lights in a soft blue to make up for it. These fill lights also don't light the interior, and don't cast shadows.