>E.g. scrolling to the bottom of the page causing a small bounce back instead of doing nothing is an absolutely information-providing animation you don't even think of as an animation. That's how you know it's good.
A bounce-back animation is bad design. Bouncing is distracting and annoying. My scroll area should not bounce unless I deliberately order it to bounce. GTK has a somewhat better solution, where it shows a animated shrinking translucent chord of a circle (or some similar shape) at the end of the scroll area. This could be considered a dedicated notification area, but it's not a good one because it overlaps whatever else is in the scroll area. Ideally, the "invalid scroll" notification should be shown in the scrollbar.