I had the same problem ... I took over responsibility for a site that was a mess. I rue the day that I re-organised it to be more logical and structured!
In Sitemaps, Google was reporting 404 errors on 29 pages that didn't exist anymore. I was struggling to think why Google was trying to crawl those legacy pages, so I used their "URL Removal" tool.
I've got a few of our obsolete pages listed there. It says:
2006-02-03 01:54:07 GMT :
removal of ......html
But it doesn't stop Google trying to crawl those pages though!
Just to check that I haven't got any links lurking in our code, I downloaded the entire site to my PC and did a text search for those URLs ... nothing.
However, now our complete cache in Google has gone missing!
My conclusion is that although we have no cache showing on Google results, they do have an old cache lying in some murky corner which they are using to try to index our current site.