QCD coherence effects are studied based on measurements of correlations
of particles with either restricted transverse momenta, pT < pTcut,
where pT is defined with respect to the thrust axis, or restricted
absolute momenta, p = |p| < pcut, using about four million hadronic Z0
decays recorded at LEP with the OPAL detector. The correlations are
analyzed in terms of normalized factorial and cumulant moments. The
analysis is inspired by analytical QCD calculations which, in
conjunction with Local Parton-Hadron Duality (LPHD), predict that, due
to colour coherence, the multiplicity distribution of particles with
restricted transverse momenta should become Poissonian as pTcut
decreases. The expected correlation pattern is indeed observed down to
pTcut ~ 1 GeV but not at lower transverse momenta. Furthermore, for pcut
-> 0 GeV a strong rise is observed in the data, in disagreement with
theoretical expectation. The Monte Carlo models reproduce well the
measurements at large pTcut and pcut but underestimate their magnitudes
at the lowest momenta. The e+e- data are also compared to the
measurements in deep-inelastic e+p collisions at HERA. It is shown that
for soft particles, the often assumed equivalence of a single hemisphere
in e+e- annihilation with the current region in the Breit frame of a
deep-inelastic collision may be misleading. Our study indicates
difficulties with the LPHD hypothesis when applied to many-particle
inclusive observables of soft hadrons.