  We have explored the evolution of a cold debris disk under the gravitational
influence of dwarf planet sized objects (DPs), both in the presence and absence
of an interior giant planet. Through detailed long-term numerical simulations,
we demonstrate that, when the giant planet is not present, DPs can stir the
eccentricities and inclinations of disk particles, in linear proportion to the
total mass of the DPs; on the other hand, when the giant planet is included in
the simulations, the stirring is approximately proportional to the mass
squared. This creates two regimes: below a disk mass threshold (defined by the
total mass of DPs), the giant planet acts as a stabilizing agent of the orbits
of cometary nucleii, diminishing the effect of the scatterers; above the
threshold, the giant contributes to the dispersion of the particles.
