I understand 'East Meath' to be all of the coastal (and near coastal) parishs/towns in Meath as follows:
Gormanstown, Ballygarth, Colp, Julianstown, Moorechurch, Bettystown (Betaghstown), Laytown, Ninch, Mornington, Donacarney ....... also maybe Duleek, Donore, Oldcastle....
I've never seen a definate answer to your question written down anywhere Bodger... but hope this helps somewhat. Kind regards, Karen