Where to register power of attorney for nri

Hi, I have a flat in Indirapuram, Ghaziabad, U.P.. I want to sell that flat. But I am not in India. I am an Indian citizen but live in USA. I have created a power of attorney for my father and got it verified/notarized by Indian embassy in USA. I am sending this PoA to my father so that he can sell my flat on my behalf. My father lives in Allahabad, U.P. Once he receives this PoA, he will have to get it registered on a 100 Rs Stamp paper. Question is: Does my father need to get this PoA registered on 100 Rs stamp paper in Allahabad where he lives? OR He will have to register this PoA in Ghaziabad where my flat is for sell?