I grew up around here and originally it was classified as Terenure, D6. According to land reg, it is still in the townland of Terenure. EA's will use land reg or post code -depends on which is best for them.
On Postcodes- Their function is to assist in mail delivery, not house valuations. An Post (P&T then) sometimes need to re-align District offices (2, 4, 5, 6 etc) to account for growth. This is what happened many years ago when Fernhill/Greentrees/Whitehall was moved from D6- to the D12 area. More recently it happened in the case of D6/D12 by the creation of D6W.
One thing is clear-Greenhills is not correct. Manor Estate (if you can find it on a map) is.