void unload(final Chunk chunk) {
        final Set<Region> unloaded = this.cache.remove(ChunkCoordinates.hash(chunk));
        if (unloaded == null) return;

        for (final Region region : unloaded) {
            final long remaining = this.references.get(region);
            this.references.put(region, remaining - 1);
            if (remaining == 1) this.catalog.deregisterOptions(region);
        }
    }