Or more precisely, not-existing everywhere. Coined from Latin roots on analogy from ubiquitous by mistakenly taking the u- part to be the "everywhere" (it's the ubiqui- instead) and replacing it with nullibi, nowhere. Probably best used humorously, but I'd love to see a scientific paper mention the nullibiquity of experimental errors.
"I have twenty years experience in deprogramming, so believe me when I warn you of the dangers of our nullibiquitous alien overlords."
---L.