In [19] it was shown that a compactly generated locally compact group G admits a finite normal series (G i ) in which the factors are compact, discrete or irreducible in the sense that no closed normal subgroup of G lies properly between G i−1 and G i . In the present article, we generalize this series to an analogous decomposition of the coset space G/H with respect to closed subgroups, where G is locally compact and H is compactly generated. This time, the irreducible factors are coset spaces G i /G i−1 where G i is compactly generated and there is no closed subgroup properly between G i−1 and G i . Such irreducible coset spaces can be thought of as a generalization of primitive actions of compactly generated locally compact groups; we establish some basic properties and discuss some sources of examples.