How can I bust a template cached plugin variable in a loop?
Left to itself, the {% cache %} tag will cache the content per-url. The problem you have is that the same url sometimes has $'s, and sometimes has GBP.

You can use the using key feature to cache based on the url and the currency:

{% cache globally using key craft.request.path ~ craft.geo.info.currency_symbol %}


(craft.geo.info.currency_symbol may not be the best disambiguator string, but this should get you started.)