Ireland (along with Italy and a few other countries) is specifically excluded on credit card insurance coverage.
http://www.mastercard.com/cardholder...insurance.html
Where you're covered: · In general, coverage is accepted worldwide, but there are exceptions.
· You may be unable to use this service in Australia, Ireland, Israel, Italy, Jamaica, or New Zealand. Please contact your car rental company before you travel.
· Coverage is not available where prohibited by law.
In general, however, rental coverage is now a feature on base level Visa, MC and Amex cards.