The “true tabernacle” in heaven is the sanctuary of the new covenant. When Christ died, the symbolic service of the earthly sanctuary ended. Since Daniel 8:14 extends down to our era, the sanctuary to which it refers must be the sanctuary of the new covenant. So the prophecy, “For two thousand three hundred days; then the sanctuary shall be cleansed,” points to the sanctuary in heaven. LF 172.2
But what is the cleansing of the sanctuary? Can there be anything in heaven that needs to be cleansed? Hebrews 9 plainly teaches the cleansing of both the earthly and the heavenly sanctuary: “According to the law almost all things are purified with blood, and without shedding of blood there is no remission. Therefore it was necessary that the copies of the things in the heavens should be purified with these [the blood of animals], but the heavenly things themselves with better sacrifices than these” (Hebrews 9:22, 23), even the precious blood of Christ. LF 172.3