".....Eight OECD nations have worldwide systems, including the U.S., Greece, Ireland, South Korea, and Mexico."
Hmmm, I am a dual UK/Irish citizen, as are millions, and was not aware of that. Certainly never done a return.
Ahhh, that's OK. For Ireland you have to be resident or domiciled during the tax year to be liable.
http://irishabroad.com/Irish-World/Expats/Moving-to-Ireland/Working/taxation/