Multi country cache problem

[Maikel Brouwer - Songteksten.nl]

Hi,

I've got the following problem. Maybe someone has a solution for it. My
site is visited by two countries (Belgium and Netherlands). I have two
different advertisement agencies to display ads for the specific
countries. This means that every page how something like this:

if ($country == 'be') {
  //display stuff
} else {
  //display other stuff)
}

The problem is that when someone from 'be' visits the page when it's not
yet cached the code in the 'be' block will be cached. When someone from
'nl' visits the page it will see the 'be' block.

I have three of those ad blocks on every page, with 500k+ pages (dynamic
content).

Thanks,
Maikel