The spell Drawmij's instant summons is cast on both a sapphire (the material component of the spell) and an object (the target of the spell) that is to be summoned by crushing the sapphire.
Normally, I would expect that casting dispel magic on the target object would end the spell. However, the last line of the spell states:
Dispel magic or a similar effect successfully applied to the sapphire ends this spell's effect.
Is this adding an additional way to dispel the spell, or is it specifying the only way to dispel it? In other words, can I dispel the spell without accessing the sapphire, or do I need to target the sapphire in order to dispel the spell?