Gaels (technically Goidils at the time) hadn't invaded Caledonia yet, so no Scots existed. Goidils had only recently conquered Mann in this period, and while there is evidence some migrated to Caledonia, the large scale invasions that would eventually form Scots hadn't occured yet.

Also, Tara wasn't a city at this time. It was just a temple complex with a small outlying town. More important were Menapia, Ivernis, Nagnata, and Eahmain Macha.