is your Irish CPL a JAR licence or a national licence?
If it is a JAR licence perhaps have a look at this, very useful site for such questions, Peter has done quite a bit of research into such matters. If it is an Irish national licence then the answer is 'in ireland only'
License Privileges, Aircraft Registers, Etc
Also - did you mean validation? as in validation of a foreign commercial license? that type of process is often a one off limited period deal, for commercial use. Presume you meant, gain a FAA 61.75 'based on' licence by getting a letter of verification of your irish licence, which will get you private but not commercial privileges in a n reg anywhere. You will need to appear at a US FSDO or find a FAA designated Foreign Pilot Examiner, needs to be done in person.