To reset store after logout with Apollo client and React, we set the Mutation component’s onCompleted prop to a function that clears the store.

For instance, we write

<Mutation
  mutation={LOGOUT_MUTATION}
  onCompleted={() => {
    sessionStorage.clear();
    client.clearStore().then(() => {
      client.resetStore();
      history.push("/login");
    });
  }}
>
  {(logout) => (
    <button
      onClick={() => {
        logout();
      }}
    >
      Logout <span>{user.userName}</span>
    </button>
  )}
</Mutation>;

to set onCompleted to a function that clears sessionStorage with

sessionStorage.clear();

Then we clear the Apollo store with

client.clearStore().then(() => {
  client.resetStore();
});