Hertz &or Avis have a clause in their T&Cs that anyone who books on a foreign Website may be required to show proof either that they live permanently in the country of the Website or at least were there when they reserved the car. I've no clue on how often they enforce this.
I tried a few years ago to book car rentals on British Websites. Usually they wanted a higher price than US Websites + LDW was automatic/ mandatory, so I guess that few UK credit cards offer intl. coverage. Also prepaid in pounds which meant a 3% forex fee for me back then.