I very much doubt that 6,000 years cycle. The Egyptian priests would most definitely have brought that to light considering they would have to have lived through two of those things.
Antedeluvian legends on the other hand are mentioned by all big civilisations and the Kemetic priests claim there have been multiple of them in the last 20,000 years. Which coincides with actual geological evidence. Especially the supposed Atlantian flood of 11,600 years ago.