Possible to get content block from another entry? I guess this isn't possible as it would mean the content is essentially a Global, but I would like to be able use a block from a matrix field from another entry. 

At the moment I have a parent page with a block of content, which I would like to replicate on all of it's child pages. I don't want to make the user repeat it on each child page, but I don't want to hardcode it.
You can query for that parent page's entry model with a new ElementCriteriaModel.

{% set mainEntry = craft.entries.id(100).first() %}

{% if mainEntry %}
    {% set matrixField = mainEntry.matrixFieldHandle %}
    {% set firstContentBlock = matrixField.type('content').first() %}

    {% if firstContentBlock %}
        {{ firstContentBlock.myRichTextFieldHandle }}
    {% endif %}
{% endif %}


Instead of using the entry's ID as the link to that entry, you can also use other parameters to query for the entry model. Here's an example using slug and section:

{% set mainEntry = craft.entries.section('news').slug('main-news').first() %}