  We argue that study of total cross section of photoabsorption and coherent
photoproduction of $\rho,\rho^{\prime}$-mesons in ultraperipheral heavy ion
collisions (UPC) is effective method to probe onset of black body limit(BBL) in
the soft and hard QCD interactions. We illustrate the expected features of the
onset of BBL using generalized vector dominance model. We show that this model
describes very well $\rho$-meson coherent photoproduction at $6 \leq E_{\gamma}
\leq 10 GeV$. In the case of $\rho$-meson production we find a UPC cross
section which is a factor $\sim 1.5 $ larger than the one found by Klein and
Nystrand. The advantages of the process of coherent dijet production to probe
onset of BBL in hard scattering regime where decomposition over the twists
becomes inapplicable are explained and relative importance of the $\gamma
+Pomeron$ and $\gamma +\gamma$ mechanisms is estimated.
