They had come to the desolation that lay before Mordor: the lasting monument to the dark labour of its slaves that should endure when all their purposes were made void; a land defiled, diseased beyond all healing — unless the Great Sea should enter in and wash it with oblivion.
There are no more uses of "oblivion" in the book.
Show samples from other sources
And if he kept his eye peeled quickly he would see himself, an instant before oblivion,
Ray Bradbury -- Fahrenheit 451
The ache inside Thomas was deep and gnawing, and he tried to sink further into oblivion.