The selection is used to filter the data set is used in the analysis. The selection should also filter and reduce the values in the attribute dialog.
E.g., if there is global selection is set to COUNTRY = US, then the filter dialog for CITY should only values, which occur also in combination with the country US. (so this means only US cities are shown).
We see use of showing the 'unavailable' values, e.g. cities outside of US, but only if they are marked in a special way, e.g. greyed out.