  The dynamical mean-field theory of the three-band model of copper-oxide
superconductors is used to calculate the doping dependence of the intensity of
the oxygen K-edge x-ray absorption spectra of high-$T_c$ copper oxide
superconductors. The model is found not to reproduce the results of a recent
experiment, suggesting that at sufficiently high doping the physics beyond the
conventional three-band model becomes important.
