Can a will be partially revoked?

In many states a will may be partially revoked automatically, by the law, in certain situations (for example, in some states, when you get divorced, any portion of your will regarding your ex-spouse is automatically revoked, but the remainder of your will remains valid). Some states take this a step further, and let you partially revoke your own will, while other states do not allow for such partial revocation. The states that do allow for partial revocation require the same steps as required for a full revocation of the will.