  We study the set $\widehat{\mathcal S}_M$ of framed smoothly slice links
which lie on the boundary of the complement of a 1-handlebody in a closed,
simply connected, smooth 4-manifold $M$. We show that $\widehat{\mathcal S}_M$
is well-defined and describe how it relates to exotic phenomena in dimension
four. In particular, in the case when $X$ is smooth, with a handle
decompositions with no 1-handles and homeomorphic to but not smoothly
embeddable in $D^4$, our results tell us that $X$ is exotic if and only if
there is a link $L\hookrightarrow S^3$ which is smoothly slice in $X$, but not
in $D^4$.
  Furthermore, we extend the notion of high genus 2-handle attachment,
introduced by Hayden and Piccirillo, to prove that exotic 4-disks that are
smoothly embeddable in $D^4$, and therefore possible counterexamples to the
smooth 4-dimensional Sch\"onflies conjecture, cannot be distinguished from
$D^4$ only by comparing the slice genus functions of links.
