Nondetection protects you from "being detected"
The exact phrasing of the spell is:
The target can't be targeted by any divination magic or perceived through magical scrying sensors.
Thus, you cannot be perceived through magical Scrying sensors. This means that even if you target a location with the Scrying spell, you are not perceived--to you, the target is both silent and invisible. You might be able to ascertain that someone is there by how the environment reacts (footprints, etc.) but you cannot see them.
It's a little less clear whether you're protected from a Clairvoyance sensor, since the text of Nondetection specifically says "scrying sensor" and not "clairvoyance sensor". However, the PHB uses the lowercase "scrying," so it's likely referring to sensors in general, and therefore you'd be invisible to a clairvoyance sensor also.