Same cache version of homepage on all subdomains for anonymous users

The easiest way to understand is to go to on-map.net or any of it's subdomains (seville.on-map.net, granada, cordoba, costadelsol, costadelaluz, etc.. - they are under the heading of Destinations in Spain).

You will see that on all the subdomains you get the same homepage/frontpage, while each should show the map, markers and listing only belonging to content associated to the specific destination-domain (some overlap!).
However, this only happens with anonymous user, when logged in all homepages appear correctly.

I have discovered that those 'fixed homepages' correspond to the first homepage to have been visited and cached by an anonymous user for each language. So if the first page I (anyone) access, as anonymous user, after flushing caches is http://costadelsol.on-map.net/nl, then this will be the homepage for our Dutch visitors also on sevilla.on-map.net, granada, costa de la luz, sierra nevada, etcetera.
Nevertheless if the first accessed (cached) italian page, after the same flush, is http://ronda.on-map.net/it then all italian visitors will see the Ronda homepage also if they go to Madrid, Barcelona or Mallorca.

I this should be solve through Domain Access error although it might be cache as well, I can't really grasp it... Any suggestions on this?

This situation has come up after a slow and troublesome change of hosting to a Drupal specific host who won't help us in this, if not paying 50 € per hour. In the old setup (not very much change) at the old host this didn't occurr. I have managed to get that former site active again under www.basiccity.info so you can compare.

Both are working under Drupal 6.17.
On-map uses Domain Access 6.x 2.5 - basiccity.info uses 6.x-2.0-rc8

Any suggestions on this?