Well you don't, for example lots of UK sites pass on 'meta data' (aka identifiable data with a bit of work)
to sites in non EU countries.
To check what is passed, you can via the ICO see where they are allowed to pass this data.
This has been happening prior to the Cloud (just a big server somewhere else to attract lazy companies to store data somewhere and we don't really give a fuck because its cheaper and we have a fast internet connection but we really didn't clue up as to when fast internet goes willy up we are fucked, but who cares we are dim suits, who NEVER listen to the techies who know, and its not our data, well yes it is, so hahaha)
Oops, my first rant, Spanky time!!