I have not found the exact location of Mount Ruby House, but believe I have found out the possible townland it was located in, and the primary resident of the house between about 1905 and 1911.
Guy's Almanac of Cork 1907 shows a Justice of the peace at the address :
Major John Creagh , Mount Ruby, Mallow appointed 1905.
A Major John Creagh J.P., presumably the same person and possibly still at the same address, is listed on the 1911 census in the townland of Annabella in the Civil Parish of Mallow.Creagh Household, Annabella
House names are not mentioned on the census, but it is one of the large houses in the townland with 12 rooms and 10 windows at front of house. Major Creagh is also listed as the owner of a gate house and another property in the same townland... so it sounds like a reasonable possibility for MountRuby House.
here's a list of the other occupants in the same townland : Annabella townland 1911 occupants
The various Guy's directories are available on the Cork Library Website at : http://www.corkpastandpresent.ie/places/streetandtradedirectories/