Da Wikipedia:
The Xindi were first referenced in Star Trek: The Next Generation episode "The Battle" (the captioning spells them "Xendi," but they were pronounced the same way). This episode was set in the Xendi Sabu star system, as Captain Picard notes in the introductory log entry. Later, Picard receives his old ship the Stargazer, and Data informs the bridge crew that a tug-ship is to take it to Xendi Starbase Nine.
De acordo com a Memória Alfa, (e a impressão que tive enquanto assistia ao episódio), os "Xendi" / Xindi não são atualmente parte da Federação, como da TNG 1x09: link
The Xendi Sabu system was a star system situated close to Federation space and the territory of the Ferengi Alliance.