It is worth searching for poor relief applications, however, particularly after a spouse has died. They often name the parish or county of origin in Ireland. Records are patchy though - Glasgow has some brilliant records at the Mitchell Library, Edinburgh virtually none.
Also, some Irish people were returned to their parish of origin in Ireland when they tried to claim poor relief in Scotland. Raymond's County Down website at www.raymondscountydownwebsite.com/html/index2.htm has a list of those returned to Ireland in 1867, 1869, and 1875-78. The database lists the parish of residency in Scotland, and the place in Ireland to where they were returned.
Chris