We present a new indexing method named ZINC (for Z-order Indexing with Nested Code) that supports efficient skyline computation for data with both totally and partially ordered attribute domains. The key innovation in ZINC is based on combining the strengths of the ZB-tree, which is the state-of-the-art index method for computing skylines involving totally ordered domains, with a novel, nested coding scheme that succinctly maps partial orders into total orders. An extensive performance evaluation demonstrates that ZINC significantly outperforms the state-of-the-art TSS indexing scheme for skyline queries.