I am certain I didn't accidentally delete anything. I purposely deleted the directory data/pages/start which contained one file called starttest.txt
I called the namespace "start" to see if it would conflict with the page (start.txt) which it didn't. But then I had no use for a namespace called "start".
I looked at the page Rene recommended
https://www.dokuwiki.org/devel:caching and tried to touch conf/local.php but it didn't have an effect.
I am a bit confused though regarding the instructions for rebuilding the cache on a single page. For example, the URL
http://my.server.com/dokuwiki/doku.php?id=start would the purge URL then be
http://my.server.com/dokuwiki/doku.php?id=start?purge=true ?
If that is correct it doesn't seem to have an effect either