In 794 , according to the Annals of Ulster , there was a serious attack on Lindisfarne 's mother-house of Iona , which was followed in 795 by raids on the northern coast of Ireland . In 794 , according to the Annals of Ulster , there was a serious attack on Lindisfarne 's mother-house of Iona , which was followed in 795 by raids upon the northern coast of Ireland .