  We use top-down gauge theory/string theory correspondence to compute
relaxation rates in strongly coupled nonconformal gauge theory plasma. We
compare models with difference mechanisms of breaking the scale invariance:
"hard breaking" (by relevant operators) and "soft breaking" (by marginal
operators). We find that the thermalization time of the transverse traceless
fluctuations of the stress-energy tensor is rather insensitive to the
mechanisms of breaking the scale invariance over a large range of the
scale-breaking parameter $\delta=\frac 13-c_s^2$. We comment on the relevance
of the results to QCD quark-gluon plasma.
