I jinxed myself
The corruption came back for a few minutes and went away. It was ONLY visible on the laptop's display.
With either a VGA cable or an HDMI cable connected to an external monitor (which ran at the same resolution as the laptop's display) there was no corruption at all. Also with the external monitor, I ran MSI Afterburner on both the nVidia GPU and the IGP and there was no artifacts. (I confirmed it was running on IGP and GPU by looking at GPU-Z and the frame rate difference between the IGP running Kombustor and the GPU running Kombustor.)
Is this a dying panel / connection to panel?