In the comments they say that "tampering"[1] is done once every year and the wiki page does not mention cleaning as an objective. Tamping is done to readjust the ballast making the track more more level and durable. (One can infer it does some cleaning as well - getting rid of the topmost dust layer)
https://www.youtube.com/watch?v=zNFUgTJR6jw seems to be the full cleaning procedure
[1] https://en.wikipedia.org/wiki/Tamping_machine