What happened to Mordor?

[zxcvbn]

Well, reading these lines from the book, I don't think Mordor's corruption was cleansed anytime in the Fourth Age.

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.

'unless the Great Sea should enter in and wash it with oblivion'. That would mean the Bibical Flood that Tolkien predicted at the end of the Fourth Age.