  We present a detailed study of kinematical and dynamical conditions necessary
for probing highly elusive three-nucleon short range correlations~(3N-SRCs) in
nuclei through inclusive electron scattering. The kinematic requirements that
should be satisfied in order to isolate 3N-SRCs in inclusive processes are
derived. We demonstrate that a sequence of two short-range NN interactions
represents the main mechanism for 3N-SRCs in inclusive processes. Within this
mechanism we predict a quadratic dependence of the inclusive cross section
ratios of nuclei to $^3$He in the 3N-SRC region to the same ratio measured in
2N-SRC domain. The extended analysis of the available data satisfying the
necessary 3N-SRC kinematical conditions is presented. This analysis provides
tantalizing signatures of scaling associated with the onset of 3N-SRC
dominance. The same data are also consistent with the prediction of the
quadratic relation between the ratios measured in the 3N and 2N-SRC regions for
nuclei ranging $4 \le A \le 197$. This agreement made it possible to extract
$a_3(A)$, the probability of 3N-SRCs relative to the A=3 nucleus. We find
$a_3(A)$ to be significantly larger in magnitude than the analogous parameter,
$a_2(A)$, for 2N-SRCs.
