  We study the phenomenon of duality in hard exclusive reactions to which QCD
factorization applies. Considering "two-photon"-like processes in the scalar
$\phi^3_E$ model and also hadron-pair production from the collisions of a real
(transversely polarized) and a highly virtual, longitudinally polarized, photon
in QCD, we identify two regimes of factorization each of them associated with a
distinct nonperturbative mechanism. One mechanism involves twist-3 Generalized
Distribution Amplitudes, whereas the other one employs leading-twist Transition
Distribution Amplitudes. In the case of the scalar $\phi^3_E$ model, we find
duality in that kinematical region where the two mechanisms overlap. In the QCD
case, the appearance of duality is sensitive to the particular nonperturbative
model applied and can, therefore, be used as an additional adjudicator.
