It's senseless to dispose of foreign capital (6)
I believe the answer is:
madrid
'foreign capital' is the definition.
(capital of Spain)
'it's senseless to dispose of' is the wordplay.
'it's senseless' becomes 'mad' (I've seen this in another clue).
'to dispose of' becomes 'rid' (to get rid of is to dispose of).
'mad'+'rid'='MADRID'
(Other definitions for madrid that I've seen before include "City with the Prado national art gallery" , "Capital of Spain since 1561" , "European capital city" , "Spanish city" , "Spanish capital" .)