  The temperature dependence of the coherence time of hole spins confined in
self-assembled (In,Ga)As/GaAs quantum dots is studied by spin mode-locking and
spin echo techniques. Coherence times limited to about a \mu s are measured for
temperatures below 8 K. For higher temperatures a fast drop occurs down to a
few ns over a 10 K range. The hole-nuclear hyperfine interaction appears too
weak to account for these limitations. We suggest that spin-orbit related
interactions are the decisive sources for hole spin decoherence.
