Methods and apparatus are described for assigning data units to a plurality of groups. A key is generated for each of the data units such that the keys corresponding to associated ones of the data units are identical. An initial hash value is generated for each of the keys. A number of techniques are described for then deterministically scrambling the initial hash values such that small bit changes in the keys will typically produce stochastically large changes in the final hash values. The data units are mapped to specific ones of the groups with reference to the scrambled hash values.