A will can be revoked by physically destroying the will.
If a will cannot be found and it was last known to be in the defendant's possession, it is presumed to be destroyed.
Just because it cannot be found does not mean that will be found to be revoked though.
A will can also be physically revoked by writing on the old will. E.g., crossing it out, writing "void" on it, etc.
In Virginia, the writing on the will must touch the writing in the will to be a valid revocation.
- Apparently this has supposedly changed.
Under UPC § 2-507(a)(2), a writing anywhere on the document can revoke it.