First, if it’s an IRBM or ICBM with a nuke warhead, you absolutely must intercept it above the atmosphere, preferably hundreds to thousands of miles away from your country’s borders. Also, the Iron Dome type of system is simply not designed to take out the much larger sized missiles that would be launched from Iran. Iron Dome does not pack the weight/payload that would be sure to take out an ICBM, even if it could hit it. Could Iron Dome score hits as a last gasp effort against ICBMs that otherwise would get through? I don’t know but I have never seen reference to that kind of testing for Iron Dome.
Unless the nuke is set off in the special way required, busting it up would produce a dirty bomb, not a nuclear explosion as intended. Are any ICBMs designed to cope with physical hits prior to arrival at point of detonation?