Ensure all the domains have http:// prefix

Use the formula:

=IF(ISERROR(FIND("//www.",A2)), MID(A2,FIND(":",A2,4)+3,FIND("/",A2,9)-FIND(":",A2,4)-3), MID(A2,FIND(":",A2,4)+7,FIND("/",A2,9)-FIND(":",A2,4)-7))

Stolen the formula from here:

You can download a template spreadsheet here:
domainfromurl2