Is the ghusl valid and the intention complete if water reaches all parts of the body, even if the intention was interrupted during the ghusl?

You may be afflicted with waswasah (whispering from Satan), so you should disregard it. Revoking the intention after completing an act of worship does not affect its validity. If ghusl (ritual bath) was performed and water reached all parts of the body, then the intention was revoked, the ghusl is valid and your worship is complete by consensus. However, revoking the intention during purification (wudu' or ghusl) is detrimental, and it becomes necessary to renew the intention for the remaining parts of the body to be purified.