In 2015, Belgium applied the law to Facebook. This means that as a country they were unhappy with a cookie which was tracking non-users of the site.
It's an example of a highly intrusive cookie that the country felt shouldn't be applied to non-users.
The Belgian Privacy Commissioner had used the EU law to file the complaint with a fine of 250,000 Euros per day for noncompliance. Facebook have since changed the cookie behaviour for Belgian internet users only.
Facebook have offices in Europe therefore they are under European law. Therefore another privacy commission in the EU could apply the law against Facebook as Belgium have.
If you are are based in the EU you must comply, regardless of your data center being from outside the EU.
It is down to the EU states own privacy/information commissioner to apply the EU law.