You can attempt to dispel or counterspell an epic spell with greater dispelling, but it's quite hard to make the dispel check: You roll 1d20+Caster Level (max +20) against DC 11 + Epic Spell's caster level. Your best result is 40, and the DC is at least 32! (dispel magic is not strong enough to dispell an epic spell, as it's best result is 30).
There is epic counterspell, which gives you +40 on the dispel check to counterspell any spell (epic or not), and superb dispelling is as greater dispelling, only that it has max +40 and deals 10d6 backlash damage. Of course, these are both epic spells.