Restrict your android activity to be accessible from other activity

I have an Android activity defined in my Manifest:

   <activity
       android:name=“com.me.myapp.myactivity">
       <intent-filter>
           <action android:name="android.intent.action.VIEW" />

           <category android:name="android.intent.category.DEFAULT" />
           <category android:name="android.intent.category.BROWSABLE" />

           <data android:scheme="myapp" />
       </intent-filter>
   </activity>

I want to restrict this activity to be accessible only to one other activity outside my app, let's call that activity "com.others.theirapp.theiractivity". How do I accomplish this restriction?

from Restrict your android activity to be accessible from other activity