[datenwolf]

> should they be scrubbing vram as well

Yes, but VRAM is a tricky beast. Modern GPUs actually have MMUs and the VRAM address layout the CPU sees may not cover the whole of the memory of the graphics card.

> What happens if I watch 2 minutes of 1080p video - wouldn't we expect all previous framebuffer data to be flushed at that point ?

No, because the video frames will be queued in a circular buffer and anything outside of that doesn't get touched.

[cesarb]

The only way I can see to reliably scrub VRAM would be to use the GPU as a "dumb framebuffer" (without video acceleration), like in the good old days. Then to scrub what was used in the session it should be enough to draw a black screen, do a page flip, and draw a black screen again.