It has been shown that the renormalization group (RG) flow connecting different vacua may occur due to the multi-trace operators in fourdimensional CFT. In the AdS/CFT set-up, the double trace operators correspond to the tachyonic scalar field living in the bulk five-dimensional AdS. In this paper, we consider the five dimensional black hole as the bulk spacetime instead of the pure AdS. In frames of the AdS/CFT correspondence, the AdS black hole is believed to describe dual CFT at finite temperature. From the AdS side, we consider the difference of energies between the two vacua by one-loop calculation for the scalar field with tachyonic mass in five-dimensional AdS black hole. In order to check the dS/CFT correspondence, the corresponding calculations are done in five-dimensional deSitter space. The difference between the two vacua is specified by the difference of the boundary conditions of the scalar field. We show that for AdS black hole, there might occur instability which could be the manifestation of the Hawking-Page phase transition. For stable phase of AdS black hole as well as for deSitter bulk, proposed c-function found beyond the leading order approximation shows the monotonic behaviour consistent with c-theorem.