Uses WinINet; 

и добавить к TButton следующий обработчик btnEmptyCache: 

Procedure TForm1.Button1Click( Sender : TObject ); 
Var 
  lpEntryInfo : PInternetCacheEntryInfo; 
  hCacheDir : LongWord; 
  dwEntrySize : LongWord; 
  dwLastError : LongWord; 
Begin 
  dwEntrySize := 0; 
  FindFirstUrlCacheEntry( NIL, TInternetCacheEntryInfo( NIL^ ), dwEntrySize ); 
  GetMem( lpEntryInfo, dwEntrySize ); 
  hCacheDir := FindFirstUrlCacheEntry( NIL, lpEntryInfo^, dwEntrySize ); 
  If ( hCacheDir <> 0 ) Then 
  DeleteUrlCacheEntry( lpEntryInfo^.lpszSourceUrlName ); 
  FreeMem( lpEntryInfo ); 
  Repeat 
  dwEntrySize := 0; 
  FindNextUrlCacheEntry( hCacheDir, TInternetCacheEntryInfo( NIL^ ), dwEntrySize ); 
  dwLastError := GetLastError(); 
  If ( GetLastError = ERROR_INSUFFICIENT_BUFFER ) Then Begin 
  GetMem( lpEntryInfo, dwEntrySize ); 
  If ( FindNextUrlCacheEntry( hCacheDir, lpEntryInfo^, dwEntrySize ) ) Then 
  DeleteUrlCacheEntry( lpEntryInfo^.lpszSourceUrlName ); 
  FreeMem(lpEntryInfo); 
  End; 
  Until ( dwLastError = ERROR_NO_MORE_ITEMS ); 
End;